1. Field of the Invention
This invention relates generally to butterfly valves, and more particularly to a mechanism for limiting undesirable inward radial movement of the seat ring in a butterfly valve of the type disclosed in commonly owned U.S. Pat. No. 3,608,861.
2. Description of the Prior Art
This invention relates to rotary fluid control valves of the butterfly type wherein a disc is mounted for rotation between the open position, in which the disc lies substantially parallel to the axis of the fluid flow channel through the valve, and the closed position in which the disc lies perpendicularly to this axis. The disc is mounted for rotation on a valve stem which is attached to the disc on one side. For convenience, said side is hereinafter referred to as the stem side of the disc. The disc cooperates with an annular flexible seat circumscribing the fluid flow channel to shut off fluid flow through the channel. More particularly, the invention relates to such valves in which the action of the internal fluid pressure acting upon the valve serves to enhance the contact pressure between the flexible seat and the disc, regardless of the direction in which fluid pressure is applied.
An example of such a butterfly valve is disclosed and claimed in commonly owned U.S. Pat. No. 3,608,861. In such a valve, the application of internal fluid pressure on the closed valve displaces both the disc and a portion of the seat ring. The disc displacement is uniform in either direction, i.e. whether the fluid pressure of a given value is applied from the right or left, the respective displacement of the disc to the right or left will be the same. The displacement of the portion of the seat ring that is exposed to the fluid in not uniform, however, since the flexibility of the valve seat is controlled by the location of fulcrums about which the seat bends. The fulcrums are at different radial distances measured from the central fluid flow axis in the valve. This displacement of fulcrums, taken together with the cross-sectional shape of the portion of the seat that contacts the disc, which is a segment of an inclined surface, enables the line pressure to enhance the sealing effectiveness between disc and seat regardless of the direction of the forces generated by such line pressure. Attention is directed to the specification of the above mentioned commonly owned patent for a more complete description of this prior art.